Guardrails are traffic barriers placed along roadsides to screen errant vehicles from hazards behind the barrier. A common guardrail in the United States is constructed using a standard steel W-beam mounted on spaced wood or steel posts. Because the W-beam functions primarily in tension when redirecting impacting vehicles, a function of the end is to provide necessary anchorage for the beam to develop necessary tensile forces. In addition, since the guardrail end represents a discontinuity in the barrier system, it is subject to being struck "head-on" by vehicles with small departure angles from the roadway. When struck in this manner, the end might spear the vehicle. Some widely used terminal designs "bury" the W-beam at the end to eliminate spearing, but this design may have shortcomings including causing problems relating to vaulting and rollover due to the vehicle riding up the end, and subsequently becoming airborne.
Another type of highway safety device is the crash cushion device. Highway agencies have been using crash cushion devices at high accident locations for a number of years. These devices absorb the energy of head-on impacts with decelerations that are not life-threatening for design conditions. Crash cushioning devices typically involve a relatively large capital investment for roadside devices. Because the number of guardrail terminals is quite large, and the impact probability low for most, the states do not have the resources to employ crash cushion devices at most guardrail ends because of their expense.
Guardrail end terminals have been developed to help absorb energy during a head-on collision by a vehicle. For example, U.S. Pat. No. 4,655,434 to Bronstad discloses such an end terminal. This type of end terminal is designed to interact with a front portion of a vehicle.
Most vehicles on highways today are fairly well configured for a head-on impact with an end terminal. The bumper, engine, and engine compartment generally provide adequate structure for the end terminal to provide an energy absorbing force without unduly impinging on the passenger compartment. The same cannot generally be said for most side impacts.
Many vehicles on the highways today have minimal structure on the sides of the vehicle that may be used to receive an energy absorbing force from an end terminal without unduly impinging on the passenger compartment. The vehicle floor structure provides the most substantial resistance during side impacts.